Configuration File Engines

Starting with v5.0.0, the routing blocks can be written in some other (well known) scripting languages and run via their embedded interpreters inside Kamailio. Known to work:

JavaScript - implemented by app_jsdt module, as “jsdt” config engine

Lua - implemented by app_lua module, as “lua” config engine

Python - implemented by app_python module, as “python” config engine

Setting a configuration engine can be done with the global setting:

cfgengine ="name"

If the name is “native” or “default”, then is own language interpreter will be used (this is same behaviour as when cfgengine is not set at all).

This setting must be after loading the module that implements the engine. For example:

...
loadmodule"app_lua.so"
...
cfgengine="lua"
...

The aim is that the runtime active part of kamailio.cfg (the routing blocks) to be implemented in an embedded scripting language. Core parameters, loading modules and modules parameters will still be set via kamailio.cfg.

Among benefits of using different scripting languages:

ability to benefit from what a well established language already provides:

more people are expected to be familiar with

an extended set of data types, expressions and statements already available

Internally, the support for implementing routing logic in an embedded language is codenamed KEMI - Kamailio EMbedded Interface.

Exporting Functions To KEMI

Because Kamailio needs to load modules in order to export useful functions to KEMI, statical wrappers to C functions implemented in other modules cannot be used, because they will introduce dependencies on each embedded interpreter for all modules.

The implementation relies on defining a set of generic functions that are exported to each embedded interpreter, which are associated at startup with a Kamailio C functions. The lookup at runtime is by an integer index, therefore very fast.

Currently the association table size is 1024 (it means that there can be maximum 1024 Kamailio C functions exported to the interpreter by a configuration file). The number can be increased, but it should be fairly enough as all kamailio.cfg functions are around 1000 and it is no real use case to load all the modules at the same time for use in production. Also, many functions may not be exported to an embedded language, as they have native alternative in the embedded language.

Each existing component of Kamailio (e.g., module), can export new functions to KEMI in the following way:

declare an array of type sr_kemi_t

register it to KEMI in mod_register() function (or at startup for core components) using sr_kemi_modules_add()

The structure sr_kemi_t is declared in Kamailio core, the file kemi.h:

Note that the exported array is ended by a sentinel of 0/NULL values for all fields.

Exported functions must take first parameter as 'sip_msg_t*' type (which is the structure with the SIP message being processed), then followed by up to 6 int or str* parameters. When SR_KEMIP_NONE is given in the array with the types of parameters, it means there is no parameter from there on (some compilers may rise warning, so it is recommended to fill all 6 items in array).

The functions exported by Kamailio core are listed inside the array _sr_kemi_core from the file kemi.c.

Not all combinations of extra (after sip_msg_t*) parameters types are supported right now - currently the are:

1 param - can be int of str*

2 params - any combination of int or str*

3 params - any combination of int or str*

4 params - all have to be str* (other combinations to be added as needed)

5 params - all have to be str* (other combinations to be added as needed)

6 params - all have to be str* (other combinations to be added as needed)

Lua Config KEMI Engine

The app_lua module must be loaded and the Lua script with routing logic must be set to its load parameter.

Inside the Lua script, following functions are relevant:

ksr_request_route() - is executed by Kamailio core every time a SIP request is received. If this function is not defined, then Kamailio will write error messages. This is equivalent of request_route {} from kamailio.cfg.

ksr_reply_route() - is executed by Kamailio core every time a SIP Response (reply) is received. If this function is not defined, then Kamailio will not write error messages. This is equivalent of reply_route {} from kamailio.cfg.

ksr_onsend_route() - is executed by Kamailio core every time a SIP request (and optionally for a response) is sent out. If this function is not defined, then Kamailio will not write error messages. This is equivalent of onsend_route {} from kamailio.cfg.

branch route callback - the name of the Lua function to be executed instead of a branch route has to be provided as parameter to KSR.tm.t_on_branch(…)

onreply route callback - the name of the Lua function to be executed instead of an onreply route has to be provided as parameter to KSR.tm.t_on_reply(…)

failure route callback - the name of the Lua function to be executed instead of a failure route has to be provided as parameter to KSR.tm.t_on_failure(…)

branch failure route callback - the name of the Lua function to be executed instead of an event route for branch failure has to be provided as parameter to KSR.tm.t_on_branch_failure(…)

TBD: the options for specific event_route blocks. Meanwhile, should work using hybrid configuration with request_route/reply_route/… in embedded interpreter and the other routing blocks in native kamailio.cfg.

KSR - provided via KEMI interface. The functions exported to KEMI are accessible as KSR.submodule.function(…). If submodule name is empty (reserved for core functions), then they are available as KSR.function(…).

Python Config KEMI Engine

The app_python module must be loaded and the Python script with routing logic must be set to its script_name parameter.

The kemi engine is built reusing the exiting app_python way of executing C code from Kamailio. In the Python script you have to declare the global mod_init() method where to instantiate an object of a class that implements the other callback methods (functions) to be executed by Kamailio.

Inside the new class, the following methods are relevant:

ksr_request_route(self, msg) - is executed by Kamailio core every time a SIP request is received. If this function is not defined, then Kamailio will write error messages. This is equivalent of request_route {} from kamailio.cfg.

ksr_reply_route(self, msg) - is executed by Kamailio core every time a SIP Response (reply) is received. If this function is not defined, then Kamailio will not write error messages. This is equivalent of reply_route {} from kamailio.cfg.

ksr_onsend_route(self, msg) - is executed by Kamailio core every time a SIP request (and optionally for a response) is sent out. If this function is not defined, then Kamailio will not write error messages. This is equivalent of onsend_route {} from kamailio.cfg.

branch route callback - the name of the Python function to be executed instead of a branch route has to be provided as parameter to KSR.tm.t_on_branch(…)

onreply route callback - the name of the Python function to be executed instead of an onreply route has to be provided as parameter to KSR.tm.t_on_reply(…)

failure route callback - the name of the Python function to be executed instead of a failure route has to be provided as parameter to KSR.tm.t_on_failure(…)

branch failure route callback - the name of the Python function to be executed instead of an event route for branch failure has to be provided as parameter to KSR.tm.t_on_branch_failure(…)

TBD: the options for specific event_route blocks. Meanwhile, should work using hybrid configuration with request_route/reply_route/… in embedded interpreter and the other routing blocks in native kamailio.cfg.

KSR - provided via KEMI. The functions exported to KEMI are accessible as KSR.submodule.function(…). If submodule name is empty (reserved for core functions), then they are available as KSR.function(…).

JavaScript Config KEMI Engine

The app_jsdt module must be loaded and the JavaScript script with routing logic must be set to its load parameter.

Inside the JavaScript script, following functions are relevant:

ksr_request_route() - is executed by Kamailio core every time a SIP request is received. If this function is not defined, then Kamailio will write error messages. This is equivalent of request_route {} from kamailio.cfg.

ksr_reply_route() - is executed by Kamailio core every time a SIP Response (reply) is received. If this function is not defined, then Kamailio will not write error messages. This is equivalent of reply_route {} from kamailio.cfg.

ksr_onsend_route() - is executed by Kamailio core every time a SIP request (and optionally for a response) is sent out. If this function is not defined, then Kamailio will not write error messages. This is equivalent of onsend_route {} from kamailio.cfg.

branch route callback - the name of the Lua function to be executed instead of a branch route has to be provided as parameter to KSR.tm.t_on_branch(…)

onreply route callback - the name of the Lua function to be executed instead of an onreply route has to be provided as parameter to KSR.tm.t_on_reply(…)

failure route callback - the name of the Lua function to be executed instead of a failure route has to be provided as parameter to KSR.tm.t_on_failure(…)

branch failure route callback - the name of the Lua function to be executed instead of an event route for branch failure has to be provided as parameter to KSR.tm.t_on_branch_failure(…)

TBD: the options for specific event_route blocks. Meanwhile, should work using hybrid configuration with request_route/reply_route/… in embedded interpreter and the other routing blocks in native kamailio.cfg.

The following objects are available inside the Lua script:

KSR - provided via KEMI interface. The functions exported to KEMI are accessible as KSR.submodule.function(…). If submodule name is empty (reserved for core functions), then they are available as KSR.function(…).

Basic IP Telephony Config Example

Some examples of configuration files using the native, Lua or Python interpreter are available in Kamailio source tree inside the examples/kemi folder - online at github:

If you define WITH_CFGLUA inside kamailio-basic-kemi.cfg or provide the command line parameter -A WITH_CFGLUA, then Kamailio will load the routing blocks in the Lua language, stored in the file kamailio-basic-kemi-lua.lua:

If you define WITH_CFGJSDT inside kamailio-basic-kemi.cfg or provide the command line parameter -A WITH_CFGJSDT, then Kamailio will load the routing blocks in the JavaScript language, stored in the file kamailio-basic-kemi-jsdt.js:

If you define WITH_CFGPYTHON inside kamailio-basic-kemi.cfg or provide the command line parameter -A WITH_CFGPYTHON, then Kamailio will load the routing blocks in the Python language, stored in the file kamailio-basic-kemi-python.py:

Combining kamailio-basic-kemi.cfg with kamailio-basic-kemi-native.cfg results more or less in the kamailio-basic.cfg from the etc/ folder in Kamailio source tree. The Lua, JavaScript and Python scripts are offering the same features, but written in another language.

Note that you need to copy these files at the location of the configuration file for your Kamailio configuration and eventually adjust the paths to them inside kamailio-basic-kemi.cfg.

Let's say you installed from sources, the config files are located inside the /usr/local/etc/kamailio/. Copy all the files listed above to that folder.

If you want to print the log messages to the terminal, add the extra parameters -E -e -ddd - this will print up to debug level which can be too verbose. Using up to info level can be better, use the extra parameters -E -e -dd .

When you have at least log level info, with kamailio-basic-kemi.cfg you will notice that a log message is printed showing the duration in microseconds of executing the main routing blocks, no matter they were in native language, Lua, JavaScript or Python. If the logs were printed to the terminal, they look like:

Depending on the scripting language used for routing blocks, the log messages start with:

NAT - for native interpreter

LUA - for LUA

JSC - for JavaScript

PYT - for Python

Again, these are specific to the config options in the kamailio-basic-kemi.cfg file – look for log_prefix inside it for more details.

Interpreters Performances

Relaying on the log messages that print the execution time for main routing blocks handling the SIP requests and responses, some statistics were gathered to see how the execution time compares for each of the interpreters.

The tests were not targeting to measure the capacity of Kamailio, but the impact of using different interpreters for same kind of features.

The system used for testing was a VirtualBox with 2GB or RAM and 2 processors, having Linux Mint as guest OS. The host was a MAC OS X running on a Mid 2012 model of Macbook Pro.

Testing was done for registrations with user authentication, using sipp tool with parameters -m 1000 -r 50 on the same VirtualBox system with Kamailio. Each test for different interpreters was doing 1000 registrations with different caller ids. Each first REGISTER was challenged for authentication, so practically there were 2000 REGISTER requests: first REGISTER being challenged with 401, the follow up was receiving 200ok as the authentication succeeded.

The values are in micro-seconds (1 / 1 000 000 of a second) and represents the average execution time, the minimum execution time and the maximum execution time for request_route{…} block (or the equivalent of).

the average was between 300 and 400 micro-seconds, resulting in a capacity of 2500 to over 3000 REGISTERs/second. CPU usage per Kamailio SIP worker process was around 1%. Again, not targeting to measure the capacity, the config runs with 4 SIP workers, increasing that will increase the capacity as database operations were involved to fetch the username and password via auth_db module.

the test was run many times, the Native and Lua execution were close to each other, many times Lua being faster, but again, at small difference

no big surprise as Lua is calling directly the C bindings and its interpreter is written also in C. With the config used in the tests, the Lua script doesn't do much of specific Lua operations, it mainly executes the functions exported by Kamailio

Python is slower comparing to Native and Lua, but not that much as one may expect. It can still deal with 2500 REGISTERs/second. Even more, some of its latency comes from the way app_modules is designed, to create a Python object from Kamailio's SIP message structure. That involves cloning (and freeing) of each SIP message to be represented as an object in Python. Lua uses the Kamailio core SIP message structure, like the Native interpreter without any overhead. Same approach should be possible for app_python, current approach is more object-oriented at expense of using more resources.

in some tests, the maximum execution time was between 5000 and 10000 micro-second, but for all interpreters, suspecting to be related to other tasks done by guest OS (which was running a web browser as well). The average didn't result in big differences, even in such cases. Also, sometimes the minimum was below 1 micro-second.

To-Do

see if same dynamic object mechanism can be implemented for Perl, Mono, Java, etc.

discuss and decide the way to generate documentation of available functions via KEMI

analyze if worth using a declarative language for specifying the exported functions and then generate necessary C code from them (could be useful for generating docs as well)